Visualization Of Coronary Vessels Research Articles

Design Optimization of A Triple-Layer Flat-Panel Detector for Three-Material Decomposition.

Spectral radiography and fluoroscopy with multi-layer flat-panel detectors (FPD) is being actively investigated in a range of clinical applications. For applications involving contrast administration, maximal contrast resolution is achieved when overlaying background anatomy is completely removed. This calls for three-material decomposition (soft tissue, bone, and contrast) enabled by measurements in three energy channels. We have previously demonstrated the feasibility of such decomposition using a triple-layer detector. While algorithmic solutions can be adopted to mitigate noise in the material basis images, in this work, we seek to fundamentally improve the conditioning of the problem through optimized system design. Design parameters include source voltage, the thickness of the top two CsI scintillators, and the thickness of two copper interstitial filters. The design objective is to minimize noise in the basis image containing contrast, chosen as gadolinium in this work to improve separation from bone. The optimized design was compared with other designs with unoptimized scintillator thickness and/or without interstitial filtration. Results show that CsI thickness optimization and interstitial filtration can significantly reduce noise in the gadolinium image by 35.7% and 42.7% respectively within a lung ROI, which in turn boosts detectability of small vessels. Gadolinium and bone signals are separated in all cases. Visualization of coronary vessels is enabled by the combining optimized system design and regularization. Results from this work demonstrate that three-material decomposition can be significantly improved with system design optimization. Optimized designs obtained from this work can inform imaging techniques selection and triple-layer detector fabrication for spectral radiography.

The impact of small motion on the visualization of coronary vessels and lesions in cardiac CT: A simulation study.

Coronary x-ray computed tomography angiography (CCTA) is used to non-invasively assess coronary artery geometry and has, combined with computational modeling, demonstrated the potential to identify physiologically significant lesions. These measurements require robust and accurate coronary imaging and delineation of vessels despite the presence of small motion. This simulation study characterizes the impact of small, uncorrected vessel drifts during data acquisition on the assessment of vessel intensity, diameter, and shape. We developed a digital phantom and simulated projection data for a clinical scanner geometry for a range of vessel drifts that can occur during relative vessel stasis (0 to 2 mm per 360° gantry rotation) for vessels between 0.2 and 3.0 mm in diameter (covering 0% through 93% stenosis of a 3 mm vessel). In addition to the impact of vessel drift, we evaluated the performance of half-scan acquisitions (relative to full-scans) over a range of gantry positions. The performance of FDK reconstructions was compared to an iterative technique and potential improvement in sampling from focal spot deflection and quarter detector offset was compared. At rest, vessel intensity and diameter were accurately obtained in vessels greater than 1.5 mm with all vessels appearing circular in shape (major-to-minor axis ratio ~1). Vessels between 1.5 and 0.2 mm in diameter demonstrated a rapid decrease in signal intensity with full width half maximum (FWHM) vessel diameters remaining above 0.75 mm as true vessel diameter decreased. Uncorrected vessel motion resulted in decreased vessel intensity, increased vessel diameter, and distortion of vessel shape. The extent of these changes depended on both the position of the gantry as well as the reconstruction approach (half- vs. full-scan). FDK reconstruction results depended on choice of filter with Ram-Lak results yielding comparable performance to an unconstrained iterative reconstruction. Focal spot deflection and quarter detector offset did not result in large changes in performance, likely due to the high sampling density near the isocenter. Despite improvement in gantry speed and acquisition of coronary images during cardiac phases that have relatively stationary vessels, small coronary drifts (0-2 mm per 360° rotation) have been reported and if uncorrected, can present challenges to visual grading and computational modeling of stenoses because vessels will appear dimmer, larger, and more ellipsoidal in shape. The impact of a particular motion depends on the gantry position, the use of half vs. full-scan acquisitions, and the reconstruction technique.

Potential Role of Cardiovascular Imaging in Improving Cardiovascular Outcome in Coronary Artery Disease.

There is increasing interest in cardiovascular imaging modalities in the detection of subclinical and clinically-manifested coronary artery disease (CAD) to improve cardiovascular outcome in these patients. SPECT/CT and PET/CT can be applied for the assessment of myocardial perfusion and myocardial blood flow (MBF) quantification in CAD detection and characterization, while CT is predominantly used to identify coronary plaque burden and epicardial narrowing. In addition, PET/CT plays an increasing role in the detection of the "vulnerable" plaque in the epicardial artery. Imaging of myocardial perfusion with SPECT, SPECT/CT and PET/CT is a mainstay in clinical practice for the identification of flow-limiting epicardial lesions and risk stratification of patients with suspected or known CAD. In this direction, the concurrent ability of PET/CT to determine regional myocardial blood flow (MBF) in ml/g/min at rest and during pharmacologically- induced hyperemic flows allows the calculation of the myocardial flow reserve (MFR) that may unravel reductions in coronary vasodilator capacity, as functional precursor of the CAD process, monitor its response to preventive medical intervention, yield important prognostic information in subclinical - and clinically-manifested CAD, and contributes to identify the flow-limiting effect of single lesions in multivessel CAD. Adding noncontrast computed-tomography (CT) measurements of coronary artery calcifications has further improved the reclassification of cardiovascular risk in asymptomatic individuals with intermediate probability of the presence of CAD. With contrast CT, the non-invasive visualization of coronary vessels, CAD-related plaque burden and stenosis has become feasible. Yet, a definite identification of the "vulnerable plaque" is still a matter of ongoing research. PET/CT in conjunction with various positron-emitting radiotracer yields promise in the detection of the "vulnerable plaque," that, however, needs further clinical evaluation in CAD patients. Multimodality imaging in cardiovascular disease is likely to further advances and refine the identification and characterization of cardiovascular pathology in the near future.

Evaluation of Coronary Stent Patency and In-Stent Restenosis with Dual-Source CT Coronary Angiography Without Heart Rate Control

Dual-source CT has excellent temporal resolution and allows good visualization of coronary vessels without heart rate control. Our aim was to evaluate the diagnostic performance of dual-source CT in the evaluation of coronary stent patency to determine whether the good temporal resolution would improve visualization of stents. Thirty-five consecutively registered patients (10 women, 25 men; mean age, 65 years) with 48 stents were examined prospectively without heart rate controlling agents. Observers evaluating image quality and patency of the stents were blinded to the results of invasive coronary angiography. In-stent restenosis was defined as more than 50% narrowing of the lumen. All stents were considered assessable for diagnosis with dual-source CT. In 85% (41/48) of the stents, image quality was good. Only two patent stents were misidentified as being stenotic. All other stents with stenosis and occlusion were correctly diagnosed. The sensitivity, specificity, positive and negative predictive values, and accuracy of dual-source CT in the detection of in-stent restenosis and occlusion were 100%, 94%, 89%, 100%, and 96%, respectively. The McNemar test result showed no statistically significant difference between the diagnostic performance of dual-source CT and that of invasive coronary angiography. The kappa indexes showed excellent intraobserver and interobserver agreement. The high temporal resolution of dual-source CT is helpful for evaluation of coronary stents without heart rate control. Further confirmation of our preliminary results may broaden the clinical indications for CT angiography as a diagnostic test for the exclusion of in-stent restenosis.

Cardiac MR in robotic heart surgery for preoperative identification of the target vessel and precise port placement--a theoretical model.

The identification of the ideal anastomosis site and the proper port placement are critical for the success of closed-chest robotic surgery. We investigated a new systematic procedure for precise port placement for TECABs. We used trigonometry and a human thoracic model to determine the optimal working angles between anastomotic plane, instruments, and endoscope. We then applied the results to seven human subjects as follows: 1. A navigation grid was located extrathoracically before cardiac MR examination. 2. The ideal anastomosis site was defined with the MR. Intrathoracic distances and angles were computed with cardiac MR software and projected onto the thorax. 3. The ideal port placement points were marked on the thorax. The optimal working angle between endoscope and instruments was 35 degrees. 0 degrees and 90 degrees angles were associated with a significant reduction in visualization, technical ease, quality and anastomosis time. The course of the LAD was identified in all seven volunteers with MR. Mean deviation of the endoscope port from the medioclavicular line was 4.3+/-2.1 cm and of the instrument ports from the anterior axillary line 8.4+/-2.4 cm. Cardiac MR in combination with the navigation grid proved suitable for the visualization of coronary vessels for individually calculating port placement points on the thorax.

Intraoperative evaluation of coronary anatomy.

Intraoperative evaluation of coronary anatomy without arteriotomy is possible with the aid of high-frequency echocardiography (HFE). The 12 MHz linear scanner can image the coronary arteries with good resolution in the transverse section and the longitudinal course. Indications are the visualization of coronary vessels, localization of stenoses and occlusions, the measurement of vessels and stenoses and the evaluation of anastomoses.